Method and apparatus for melting and casing metal

ABSTRACT

A system for producing metal castings wherein molten metal is introduced into a preheated mold and then directionally solidified by withdrawing heat from the bottom of the mold. The system involves the location of a crucible containing solid metal on top of a mold and positioning the arrangement in a furnace. The heating mechanisms of the furnace are utilized for melting the metal and also for preheating the mold. By providing for discharge of the metal from the bottom of the crucible, the molten metal is maintained in the crucible until such time as casting is desired at which time the crucible is either tilted or lifted to permit the metal to flow through an opening in the bottom of the crucible and into the mold passages communicating with the top surface of the mold.

United States Patent [1 1 Tingquist et a1.

[451 Oct. 15, 1974 METHOD AND APPARATUS FOR MELTING AND CASING METAL[75] Inventors: Stanley C. Tingquist, Sparta;

Edward G. Laux, Wayne, both of NJ.

[73] Assignee: Howmet Corporation, Greenwich,

Conn.

22 Filed: Feh.21, 1973 (21] Appl. No.: 334,264

Primary Examiner-J. Spencer Overholser Assistant Examiner.lohn E.Roethel Attorney, Agent, or FirmMcDougall, Hersh & Scott [57] ABSTRACT Asystem for producing metal castings wherein molten metal isintroducedinto a preheated mold and then directionally solidified bywithdrawing heat from the bottom of the mold. The system involves thelocation of a crucible containing solid metal on top of a mold andpositioning the arrangement in a furnace. The heating mechanisms of thefurnace are utilized for melting the metal and also for preheating themold. By providing for discharge of the metal from the bottom of thecrucible, the molten metal is maintained in the crucible until such timeas casting is desired at which time the crucible is either tilted orlifted to permit the metal to flow through an opening in the bottom ofthe crucible and into the mold passages communicating with the topsurface of the mold.

PATENIEBUBI 1 5x914 SHEU 10F 2 III 11/11/111 Ill/ll (1)1! lfr FIG, 1;

METHOD AND APPARATUS FOR MELTING AND CASING METAL This invention relatesto improvements in metal casting techniques. in particular, theinvention is directed to a method and apparatus for accomplishingmelting and casting of metal with the metal being directionallysolidifed to produce castings having desired directional properties.

The production of directionally solidified castings is well-known. Thus,many techniques have been developed for controlling the grain structureand orientation of cast metal whereby the properties of a casting can bemaintained at the most desirable levels in a direction which willundergo the greatest stress during use. In a typical application,directionally solidified casting techniques are employed in theproduction of jet engine blades and vanes from high temperature alloys.Directionally solidified or so-called columnar structures have beenfound to be superior for high temperature operation, particularly withrespect to fracture resistance and ductility under creep loadingconditions. High temperature nickel base and cobalt base alloys aretypically cast in this manner in the production of jet engine blades andvanes.

The production of directionally solidified castings generally involvesthe pouring of molten metal into a mold which is supported on a chillplate or other heat conductive means. Heat is extracted unidirectionallyfrom the mold whereby the crystal structure of the casting will beperpendicular to the mold support.

In practice, the molds may be preheated in a susceptor heating chamber.After pouring, the unidirectional withdrawal of heat is often controlledby controlling the application of heat to the mold in the heatingchamber. For example, the mold may be gradually withdrawn from theheating chamber thereby gradually eliminating application of heat to themold walls.

Vacuum or inert atmosphere casting equipment is usually employed, and toimprove the efficiency of the operation, the melting of the metal isconducted in the same furnace. In order to provide space for melting,pouring and casting, a relatively large furnace, and accordingly, arelatively great investment is involved. The need for two power suppliesfor melting and casting is one item which leads to the high cost.

The prior art techniques typically involve induction melting operationswhich means that the metal is being continuously stirred. This makes itdifficult to separate any dross formation from the metal prior tocasting. In view of these and other considerations, it is clearlydesirable to simplify casting operations of this type while alsoimproving the quality of the cast products.

It is a general object of this invention to provide an improved processfor the melting and casting of metals.

lt is a more specific object of this invention to provide an improvedprocess for the melting of metals such as nickel and cobalt base alloysdesigned for high temperature applications, the process also includingthe casting of the metals to achieve directional solidification thereof.

It is a still further object of this invention to provide an improvedapparatus for achieving melting and casting as set forth in theforegoing objects.

These and other objects of this invention will appear hereinafter andfor purposes of illustration, but not of limitation, specificembodiments of the invention are shown in the accompanying drawings inwhich:

FlG. l is a schematic illustration in vertical section of a furnaceconstruction adapted for the practice of this invention;

FIG. 2 is a schematic vertical sectional view illustrating a mold andcrucible arrangement associated with a furnace construction inaccordance with the concepts of this invention; and,

FIG. 3 is a schematic vertical sectional view illustrat ing a mold andcrucible construction in the pouring stage of an arrangementincorporating features of the invention.

The system of the invention generally relates to a method and apparatusdesigned for the melting of metal and the casting of the metal in amold. The invention is particularly concerned with the melting andcasting of alloys such as high temperature nickel and cobalt base alloyswhich are advantageously cast by means of directional solidificationtechniques.

The apparatus of the invention involves means for supporting a mold, thesupporting means preferably comprising a chill plate or the like forachieving the withdrawal of heat from the bottom of the mold. The molddefines an upper surface, and a passage leading to a mold cavitycommunicates with this upper surface whereby molten metal can be pouredonto the upper surface and then passed into the mold cavity.

The procedure of the invention involves the location of a meltingcrucible directly on the top surface of the mold. This crucible definesa bottom wall which has at least one opening for communication with theinterior of the crucible. By providing a flat upper surface for the moldand a flat bottom wall for the crucible, the engagement of the flatwalls of the crucible and mold will have the effect of sealing thisopening so that molten metal in the crucible will not normally flowthrough this opening.

A spherical or conical shaped insert or projection in the mold couldalso be utilized to stopper the metal until casting is desired. Othermethods of stoppering the metal for bottom pour could also beincorporated as part of the invention.

The invention involves locating the mold and crucible combination in afurnace whereby metal contained in the crucible can be heated above itsmelting point. Once the metal is in a molten state, the sealing orstoppering engagement referred to may be broken by tilting the crucible.This allows the metal to flow out of the crucible onto the mold surfaceand then into the mold cavity. In accordance with accepted practice, themold is preheated, and heat is withdrawn from the metal, at least in theinitial stages of metal solidification, only from the bottom of themold. The furnace heating means or other structure may be utilized forinsuring the desired directional solidification. Discharge of the moltenmetal could also be accomplished by raising the crucible or withdrawingthe mold away from the crucible.

The accompanying drawings provide an illustration of a system adaptedfor use in accordance with the concepts of the invention. FIG. 1illustrates a housing arrangement including an upper housing 10 and alower housing 12. The alloys which are most advantageously employed inthe practice of the invention are melted and cast in a vacuum or in aninert atmosphere, and

conduits 14 are provided for achieving these conditions.

The upper housing encloses an induction furnace 16 including inductioncoil 18. The coil is located in surrounding relationship with refractorywall 20, and a radiation liner 22 is provided. The furnace constructionis thus of the susceptor type with the coil 18 generating heat in theliner 22, this heat in turn being radiated inwardly. A furnace cover 24defines a hole 26 which permits visual access to the furnace interiorthrough the viewing window 28 formed in the top wall of the upperhousing 10. This arrangement may be utilized, for example, for takingtemperature readings with an optical pyrometer. It will be appreciatedthat a resistance heated-furnace or other means for generating heat mayalso be utilized.

A chill plate 30 is provided for supporting a mold 32 relative to thefurnace. This chill plate is provided with water cooling coils 34 toenhance the withdrawal of heat during operation of the system. A shield36 surrounded by water cooling coils 38 is adapted to be positionedaround the mold 32 upon lowering of the mold again to provide a meansfor controlling the direction of heat withdrawal from the mold. Thechill plate is supported on rod 40 which is received within cylinder 42,and this rod is thereby reciprocally driven for gradually raising andlowering the chill plate and associated mold.

A flapper valve 44 is provided to permit isolation of the melt chamberfrom the loading chamber to permit a vacuum or inert atmosphere aroundthe furnace while molds are being transferred. This provides for betterefficiency of operation by eliminating the necessity of cooling thefurnace between cycles.

FIG. 2 illustrates a mold 32 supported on chill plate 30, this moldcomprising a shell mold produced by building up layers of moldingmaterial around a disposable pattern. Mold cavities 46 are definedwithin the mold, ane these cavities communicate with the top of the moldthrough passages 48. lt will be noted that the cavities 46 extenddirectly to the upper surface 50 of the chill plate 30 wherebysolidification of metal poured into the mold will be initiated at thebottom of the mold. In accordance with standard techniques, thecontinued withdrawal of heat in this direction will result in theformation of columnar grains in a direction perpendicular to the surface50.

The upper portion of the mold 32 defines a flat centrally locatedsurface 52 surrounded by upstanding walls 54. This combination comprisesa bowl or dishshaped area which is dimensioned to receive a meltingcrucible 56.

The crucible 56 defines a flat bottom wall 58 adapted to engage thesurface 52 of the mold. An outlet opening 60 is defined by the bottomwall of the crucible whereby molten metal is adapted to be pouredthrough the bottom of the crucible. The crucible receives a solid charge62 of metal alloy to be cast whereby parts can be obtained in accordancewith the configurations defined by the mold cavities 46.

In the arrangement shown in FlG. 2, the crucible 56 is initially locatedopposite the lower section of coils 18. With full power applied to thecoils, the crucible is brought to a temperature sufficient to melt themetal. The platform 30 is then raised to bring the mold 32 into theheated zone whereby the mold can be brought to temperature. Thisadditional heating period serves to raise or at least maintain the metaltemperature while stabilizing the mold temperature in preparation forcasting.

To provide an alternative operating technique, the furnace inductioncoils l8are divided into an upper section 64 and a lower section 66.With the crucible 56 and mold 32 located as shown in FIG. 3, full poweris applied to the upper section 64 for purposes of melting the metal 62within the crucible 56. At or near the completion of the meltingoperation, power is applied to both sections 64 and 66. This arrangementpermits preheating of the mold while maintaining the metal in the moltenstate.

As indicated, the engagement of the respective flat surfaces of thecrucible and mold effectively prevents passage of molten metal throughthe opening 60 whereby the melting and preheating operations can becompleted without passage of metal into the mold. This provides a simpleand efficient technique but, as explained, other stoppering methods areavailable.

When the mold has been preheated to the proper level, a crucible tiltingconstruction is brought into operation. The tilting constructionconsists of a pivotally mounted arm 68 which is attached to an operatingrod 70, the latter being accessible on the exterior of the upper housing10. By pulling on the rod 70, the end of the arm 68 will move intoengagement with crucible 56 thereby tilting the crucible as illustratedin FIG. 3. When this tilting occurs, the molten metal will flow throughthe opening 60 and into the mold cavity 46. The dish-shaped arrangementprovided by the upstanding walls 54 of the mold serves to avoid spillingof molten metal. A baffle 72 may be attached to the top of the mold,this baffle serving as a splash plate while also tending to insulate theinterior of the furnace relative to the upper housing, particularly withthe mold 32 in the lower position shown in F IG. 2. The baffle may be offlexible material to facilitate raising and lowering of the mold.

The structures illustrated are completely suitable for achievingdirectional solidification in accordance with accepted practice. Thechill plate 30 provides for withdrawal of heat from the bottom of themold, and the induction coils serve to maintain the mold in a heatedstate to inhibit withdrawal of heat laterally. As the initialsolidification takes place, the plate 30 may be gradually loweredthereby gradually withdrawing the mold from the influence of the furnacecoils. The withdrawal of heat may be further accelerated due to theinfluence of the water cooled shield 36 which is encountered as the moldis lowered.

In preparing molds for use in the practice of the invention, it isimportant to provide a very flat surface in the area 52, and this can bemost readily accomplished by utilizing a metal disc in the wax patternemployed for producing the shell mold. Thus, the wax pattern is formedaround the disc whereby the disc will be located in the area of the molddish portions. The shell mold surface which forms over the metal dischas the desired flatness for mating with the flat bottom of thecrucible.

In a typical operation involving the casting of vanes and blades fromthe nickel base alloy PWA-l422, an alloy manufactured by Pratt andWhitney, 20 pounds of metal charge were located in a crucible. Thecrucible was heated for approximately 45 minutes to achieve atemperature of 2900 F. and melting of the charge. A

2-zone 14-inch lD susceptor furnace having a 50 kw power supply wasemployed. With full power applied to the entire furnace coil, the metaltemperature was raised and the mold brought to temperature. Upon tiltingof the crucible, the metal entered the mold by passing through athree-fourth inch diameter hole formed in the bottom of the crucible andcontrolled solidification follows. The total time cycle for theseoperations is typically about three hours.

In the practice of the invention, a furnace chamber approximatelyone-third the volume conventionally required for a directionalsolidification casting furnace is required. This, of course, reducesinitial cost of the furnace, high frequency power supplies therefor,pumps, controls, etc., and maintenance costs are also significantlyreduced. It has been found that castings formed have been totallysatisfactory from the standpoint of grain structure and physicalproperties.

The melting and casting procedures involved in the practice of theinvention are advantageous since the static melting results in fewerreaction products while most non-metallics formed have an opportunity ofrising to the top of the melt. Since the techniques involve bottompouring, fewer non-metallics will be carried into the mold cavity. Theprocedures permit the utilization of a clean crucible with each meltwhich also mini mizes contamination of the cast parts. The techniquesare also quite adaptable to automation in view of the simplicity of theoperation, and since the operation lends itself to cycle controls.

It will be understood that various changes and modifications may be madein the above described system which provide the characteristics of theinvention without departing from the spirit thereof particularly asdefined in the following claims.

That which is claimed is:

1. In an apparatus for producing castings wherein molten metal isintroduced into a preheated mold and the metal is directionallysolidified by withdrawing heat from the bottom of the mold, theimprovement wherein said mold defines a flat upper surface, a cruciblehaving a flat bottom wall supported on said surface with said metalbeing contained in said crucible for melting of the metal while thecrucible is supported on said surface, an opening defined by the bottomwall of said crucible, the engagement of said flat upper surface andflat bottom wall normally preventing passage of metal through saidopening, at least one passage defined by said mold and communicatingwith said surface of the mold for the passage of molten metal into themold, and means for tipping said crucible whereby molten metal thereinpasses through said crucible opening into said top surface for passageinto said mold.

2. An apparatus in accordance with claim 1 wherein said mold is providedwith upstanding side walls in surrounding relationship relative to saidflat surface for containing molten metal on said flat surface. J

3. An apparatus in accordance with claim 1 including a furnace forreceiving said mold and associated crucible, said furnace includingheating means for melting metal in said crucible and for preheating saidmold.

4. An apparatus in accordance with claim 3 wherein said heating meanscomprise first and second heating means with the first heating meansoperating to melt said metal and with the second heating means operatingto preheat said mold.

5. An apparatus in accordance with claim 4 wherein said heating meanscomprise induction coils divided into an upper and lower section, saidcrucible being located within the confines of the upper coil section andmeans for operating the upper coil section independently of the lowercoil section for melting the metal in said crucible, and means forthereafter operating the lower coil section for preheating the moldwhile maintaining the metal in said crucible in a molten state.

6. An apparatus in accordance with claim 3 including a support for saidmold, means for raising and lowering said support, means for positioningsaid support in a lower position for locating said crucible in saidfurnace for melting of the metal within the crucible, and means forthereafter operating said support to raise the mold and crucible intothe furnace for preheating of the mold while maintaining the metal in amolten state.

7. An apparatus in accordance with claim 3 wherein said means fortilting said crucible comprise a rod extending through the wall of saidfurnace for engagement with the crucible.

8. An apparatus in accordance with claim 7 including a housingsurrounding said furnace, and a rod extension extending outwardly of thehousing for operating said rod.

9. An apparatus in accordance with claim 8 including means for creatinga vacuum within said housing whereby said metal is melted and cast undervacuum conditions.

10. An apparatus in accordance with claim 3 wherein said furnacecomprises a susceptor-type furnace, said heating means includinginduction coils, and said furnace including an inner liner in which heatis generated by said induction coils, the melting and preheatingoccurring by radiation from said liner.

11. In a method for the production of castings wherein molten metal isintroduced into a preheated mold and the metal is thereafterdirectionally solidified by withdrawing heat from the bottom of themold, the improvement comprising the steps of locating the metal in acrucible, positioning the crucible on top of said mold, providing apassage at the bottom of said crucible for providing communicationbetween the crucible and mold, normally sealing said passage, locatingthe crucible and mold in a furnace, heating the crucible to melt themetal therein while the crucible remains positioned on said mold,heating the mold to preheat the mold, tipping said crucible after themelting of the metal to break the sealing of said passage for therebydelivering metal from said crucible into said mold, and directionallysolidifying the metal within said mold.

12. In a method for the production of castings wherein molten metal isintroduced into a preheated mold and the metal is thereafterdirectionally solidified by withdrawing heat from the bottom of themold, the improvement comprising the steps of locating the metal in acrucible, positioning the crucible on top of said mold, said crucibledefining a flat bottom wall and said mold defining a fiat top surface,said crucible being supported by the mold by disposing said bottom wallon said top surface, locating the crucible and mold in a furnace,heating the crucible to melt the metal therein, heating the mold topreheat the mold, said crucible defining an opening in said bottom wallfor the discharge of molten metal therethrough and said mold defining apassage communicating with said top surface for the movement of moltenmetal into said mold, the engagement of said bottom wall with said topsurface normally preventing passage of molten metal through said openingin said bottom wall, and including the step of tilting said crucibleupon completion of the melting for delivering metal from said crucibleinto said mold, and directionally solidifying the metal within saidmold.

13. A method in accordance with claim 12 including heating meansassociated with said furnace, operating the heating means for meltingthe metal in said crucible; and thereafter operating the heating meansfor preheating said mold while maintaining said metal in a molten state.

14. A method in accordance with claim 13 including the step of locatingsaid mold and crucible on a movable platform, positioning the cruciblewithin said furance by means of said platform for melting of metalwithin the crucible, and thereafter raising said platform to positionbeyond the mold and crucible within the furnace.

15. A method in accordance with claim 13 wherein said heating meanscomprise independently operable first and second sections, operating thefirst section for melting metal within the crucible, and thereafteroperating the second section and preheating said mold.

16. A method in accordance with claim 11 wherein said furnace comprisesa susceptor furnace, said melting and preheating being accomplished byradiating heat to said crucible and mold.

1. In an apparatus for producing castings wherein molten metal isintroduced into a preheated mold and the metal is directionallysolidified by withdrawing heat from the bottom of the mold, theimprovement wherein said mold defines a flat upper surface, a cruciblehaving a flat bottom wall supported on said surface with said metalbeing contained in said crucible for melting of the metal while thecrucible is supported on said surface, an opening defined by the bottomwall of said crucible, the engagement of said flat upper surface andflat bottom wall normally preventing passage of metal through saidopening, at least one passage defined by said mold and communicatingwith said surface of the mold for the passage of molten metal into themold, and means for tipping said crucible whereby molten metal thereinpasses through said crucible opening into said top surface for passageinto said mold.
 2. An apparatus in accordance with claim 1 wherein saidmold is provided with upstanding side walls in surrounding relationshiprelative to said flat surface for containing molten metal on said flatsurface.
 3. An apparatus in accordance with claim 1 including a furnacefor receiving said mold and associated crucible, said furnace includingheating means for melting metal in said crucible and for preheating saidmold.
 4. An apparatus in accordance with claim 3 wherein said heatingmeans comprise first and second heating means with the first heatingmeans operating to melt said metal and with the second heating meansoperating to preheat said mold.
 5. An apparatus in accordance with claim4 wherein said heating means comprise induction coils divided into anupper and lower section, said crucible being located within the confinesof the upper coil section and means for operating the upper coil sectionindependently of the lower coil section for melting the metal in saidcrucible, and means for thereafter operating the lower coil section forpreheating the mold while maintaining the metal in said crucible in amolten state.
 6. An apparatus in accordance with claim 3 including asupport for said mold, means for raising and lowering said support,means for positioning said support in a lower position for locating saidcrucible in said furnace for melting of the metal within the crucible,and means for thereafter operating said support to raise the mold andcrucible into the furnace for preheating of the mold while maintainingthe metal in a molten state.
 7. An apparatus in accordance with claim 3wherein said means for tilting said crucible comprise a rod extendingthrough the wall of said furnace for engagement with the crucible.
 8. Anapparatus in accordance with claim 7 including a housing surroundingsaid furnace, and a rod extension extending outwardly of the housing foroperating said rod.
 9. An apparatus in accordance with claim 8 includingmeans for creating a vacuum within said housing whereby said metal ismelted and cast under vacuum conditions.
 10. An apparatus in accordancewith claim 3 wherein said furnace comprises a susceptor-type furnace,said heating means including induction coils, and said furnace includingan inner liner in which heat is generated by said induction coils, themElting and preheating occurring by radiation from said liner.
 11. In amethod for the production of castings wherein molten metal is introducedinto a preheated mold and the metal is thereafter directionallysolidified by withdrawing heat from the bottom of the mold, theimprovement comprising the steps of locating the metal in a crucible,positioning the crucible on top of said mold, providing a passage at thebottom of said crucible for providing communication between the crucibleand mold, normally sealing said passage, locating the crucible and moldin a furnace, heating the crucible to melt the metal therein while thecrucible remains positioned on said mold, heating the mold to preheatthe mold, tipping said crucible after the melting of the metal to breakthe sealing of said passage for thereby delivering metal from saidcrucible into said mold, and directionally solidifying the metal withinsaid mold.
 12. In a method for the production of castings wherein moltenmetal is introduced into a preheated mold and the metal is thereafterdirectionally solidified by withdrawing heat from the bottom of themold, the improvement comprising the steps of locating the metal in acrucible, positioning the crucible on top of said mold, said crucibledefining a flat bottom wall and said mold defining a flat top surface,said crucible being supported by the mold by disposing said bottom wallon said top surface, locating the crucible and mold in a furnace,heating the crucible to melt the metal therein, heating the mold topreheat the mold, said crucible defining an opening in said bottom wallfor the discharge of molten metal therethrough and said mold defining apassage communicating with said top surface for the movement of moltenmetal into said mold, the engagement of said bottom wall with said topsurface normally preventing passage of molten metal through said openingin said bottom wall, and including the step of tilting said crucibleupon completion of the melting for delivering metal from said crucibleinto said mold, and directionally solidifying the metal within saidmold.
 13. A method in accordance with claim 12 including heating meansassociated with said furnace, operating the heating means for meltingthe metal in said crucible, and thereafter operating the heating meansfor preheating said mold while maintaining said metal in a molten state.14. A method in accordance with claim 13 including the step of locatingsaid mold and crucible on a movable platform, positioning the cruciblewithin said furance by means of said platform for melting of metalwithin the crucible, and thereafter raising said platform to positionbeyond the mold and crucible within the furnace.
 15. A method inaccordance with claim 13 wherein said heating means compriseindependently operable first and second sections, operating the firstsection for melting metal within the crucible, and thereafter operatingthe second section and preheating said mold.
 16. A method in accordancewith claim 11 wherein said furnace comprises a susceptor furnace, saidmelting and preheating being accomplished by radiating heat to saidcrucible and mold.